Screw Compressor

ABSTRACT

A screw compressor that enhances performance of a compressor main unit and a motor is provided. The screw compressor includes an oil-injected compressor main unit that compresses air with injecting oil in a compression chamber and an axial-gap motor that drives the compressor main unit. A male rotor of the compressor main unit has a suction-side shaft portion connected coaxially with a rotor shaft of the motor. The screw compressor further includes a suction-side bearing that rotatably supports the suction-side shaft portion of the male rotor. The suction-side bearing restricts axial movement of the suction-side shaft portion and bears a radial load and axial loads in both directions.

TECHNICAL FIELD

The present invention relates generally to screw compressors including liquid-injected compressor main units and axial-gap motors that drive the compressor main units and, more particularly, to a screw compressor in which a screw rotor of a compressor main unit is coaxially connected with a rotary shaft of a motor.

BACKGROUND ART

Patent Document 1 discloses a screw compressor including a liquid-injected compressor main unit and a radial-gap motor that drives the compressor main unit. The following details the screw compressor.

The radial-gap motor includes a rotor shaft, a rotor mounted on the rotor shaft, and a stator spaced apart from the rotor in a radial direction. The rotor shaft is rotated by magnetic action of the stator and the rotor.

The compressor main unit includes a pair of intermeshing male and female screw rotors. One of the screw rotors is coaxially connected with the rotor shaft of the motor. Rotation of the rotor shaft of the motor causes the one of the screw rotors to rotate, which, in turn, rotates the other of the screw rotors in mesh with the one of the screw rotors. As the pair of screw rotors rotates, compression chambers defined by tooth grooves of the screw rotors and an inner wall of a casing move in an axial direction. The compression chamber draws in gas via a suction port (opening) on one side in the axial direction and compresses the gas to thereby discharge the compressed gas via a discharge port (opening) on the other side in the axial direction.

The liquid-injected compressor main unit injects a liquid into the compression chamber. The liquid injected in the compression chamber seals gaps in the compression chamber (specifically, a gap between the screw rotors and a gap between the screw rotor and the casing) and cools the compressed gas.

The screw rotors each include a tooth portion having a plurality of spiral teeth, a suction-side shaft portion (motor-side shaft portion) connected with one side in the axial direction of the tooth portion (suction side, or the motor side), and a discharge-side shaft portion (opposite-side shaft portion) connected with the other side in the axial direction of the tooth portion (discharge side, or the side opposite to the motor). As described previously, the suction-side shaft portion of one screw rotor is connected coaxially with the rotor shaft of the motor.

The suction-side shaft portion of each screw rotor is rotatably supported by a plurality of suction-side bearings. The discharge-side shaft portion of each screw rotor is rotatably supported by a plurality of discharge-side bearings. The discharge-side bearings are a plurality of angular ball bearings held at fixed positions inside the casing. The discharge-side bearings restrict axial movement of the discharge-side shaft portion of the screw rotor and bear a radial load and axial loads in both directions (specifically, a forward direction extending from the discharge side toward the suction side and a reverse direction extending from the suction side toward the discharge side). The suction-side bearings are a plurality of angular ball bearings held axially movably in the casing. The suction-side bearings permit axial movement of the suction-side shaft portion of the screw rotor and support the radial load and the axial load in the forward direction.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP-2004-150412-A (see FIGS. 1 to 3.)

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

For a reason of size reduction, for example, adoption of an axial-gap motor in place of the radial-gap motor described above is being studied. The axial-gap motor includes a rotor shaft, at least one rotor mounted on the rotor shaft, and at least one stator spaced apart from the rotor in the axial direction. The rotor shaft is rotated by magnetic action of the stator and the rotor.

As in the configuration disclosed in Patent Document 1, the suction-side shaft portion of one screw rotor may be connected coaxially with the rotor shaft of the axial-gap motor. Additionally, as in the configuration disclosed in Patent Document 1, the discharge-side bearings may restrict axial movement of the discharge-side shaft portion (opposite-side shaft portion) of the screw rotor and the suction-side bearings may permit axial movement of the suction-side shaft portion (motor-side shaft portion) of the screw rotor. The foregoing arrangements, however, pose the following problem.

The screw rotor expands by compression heat and the rotor shaft of the motor expands by heat generated by the motor. The restriction of the axial movement of the discharge-side shaft portion of the screw rotor can considerably reduce changes in the gap between a discharge-side end face of the tooth portion of the screw rotor and a wall surface of the casing. Performance of the compressor main unit can thereby be enhanced. Meanwhile, a gap between the rotor and the stator of the motor is affected by not only the thermal expansion of the rotor shaft of the motor, but also the thermal expansion of the screw rotor, resulting in large changes in the gap. Thus, performance of the motor is degraded.

The present invention has been accomplished in light of such circumstances and one of the problems to be solved is to enhance performance of the compressor main unit and the motor by reducing changes in the gap between the discharge-side end face of the tooth portion of the screw rotor and the wall surface of the casing and in the gap between the rotor and the stator of the motor.

Means for Solving the Problem

To solve the foregoing problem, configurations defined in the scope of the claims are applied. The present invention includes a plurality of means for solving the problem. One exemplary aspect of the present invention provides a screw compressor including a liquid-injected compressor main unit that includes a screw rotor and compresses gas with injecting liquid in a compression chamber defined by a tooth groove of the screw rotor and an axial-gap motor that drives the compressor main unit. The screw rotor has a motor-side shaft portion connected coaxially with a rotor shaft of the motor. The screw compressor includes a bearing that rotatably supports the motor-side shaft portion of the screw rotor. In this screw compressor, the bearing restricts axial movement of the motor-side shaft portion and bears a radial load and axial loads in both directions.

Effects of the Invention

The aspect of the present invention can reduce changes in a gap between a discharge-side end face of a tooth portion of the screw rotor and a wall surface of a casing and in a gap between the rotor and the stator of the motor, to thereby enhance performance of the compressor main unit and the motor.

Objects, configurations, and effects other than those described above will become apparent from the following description of embodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a vertical cross-sectional view of a configuration of a screw compressor according to a first embodiment of the present invention, depicting a rated operation state of the compressor.

FIG. 2 is a vertical cross-sectional view of a configuration of the screw compressor according to the first embodiment of the present invention, depicting a stationary state of the compressor.

FIG. 3 is a vertical cross-sectional view of a configuration of a screw compressor according to a first modification of the present invention, depicting a stationary state of the compressor.

FIG. 4 is a vertical cross-sectional view of a configuration of a screw compressor according to a second modification of the present invention, depicting a stationary state of the compressor.

FIG. 5 is a vertical cross-sectional view of a configuration of a screw compressor according to a second embodiment of the present invention, depicting a rated operation state of the compressor.

MODES FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIGS. 1 and 2 are vertical cross-sectional views of configurations of a screw compressor according to the present embodiment. FIG. 1 depicts a rated operation state (high temperature state) of the compressor. FIG. 2 depicts a stationary state (room temperature state) of the compressor.

The screw compressor of the present embodiment includes an oil-injected compressor main unit 1 and a radial-gap motor 2, which drives the compressor main unit 1. The compressor main unit 1 is integrated with the motor 2. Specifically, the compressor main unit 1 and the motor 2 are disposed vertically such that screw rotors of the compressor main unit 1 and a rotor shaft of the motor 2 to be described later extend in the vertical direction. The motor 2 is disposed on the upper side of the compressor main unit 1.

The motor 2 includes a rotor shaft (shaft) 3, a rotor 4A, a rotor 4B, a stator 5, and a motor casing 6. The rotor 4A is mounted on an output side (side adjacent to the compressor main unit 1) of the rotor shaft 3. The rotor 4B is mounted on a non-output side (side opposite to the compressor main unit 1) of the rotor shaft 3. The stator 5 is disposed between the rotors 4A and 4B so as to be spaced axially apart from the rotors 4A and 4B. The motor casing 6 houses thereinside the rotors 4A and 4B and the stator 5 and supports the stator 5.

As depicted in the figure, the motor casing 6 includes a motor main casing and an end cover removably mounted in an upper end opening of the motor main casing. The rotors 4A and 4B are each a permanent magnet type rotor, for example. The stator 5 is a winding type stator, for example. The rotor shaft 3 is rotated by magnetic action of the rotors 4A and 4B and the stator 5.

The compressor main unit 1 includes a pair of intermeshing male and female screw rotors (specifically, a male rotor 7 and a female rotor not depicted) and a compressor main unit casing 8, which houses thereinside the screw rotors. Tooth grooves in the screw rotors and an inner wall of the compressor main unit casing 8 define compression chambers 9. The compressor main unit casing 8 includes a main casing 10 and a suction-side casing 11, which is coupled with an upper side (suction side) of the main casing 10. The suction-side casing 11 is coupled with the motor main casing.

The male rotor 7 is coaxially connected with the rotor shaft 3 of the motor 2. Rotation of the rotor shaft 3 of the motor 2 causes the male rotor 7 to rotate and the female rotor in mesh with the male rotor 7 to rotate. The rotation of the male rotor 7 and the female rotor causes the compression chamber 9 to move in the axial direction. The compression chamber 9 draws in air (gas) from a suction flow path 13 via a suction port 12 (opening) on one side in the axial direction (the side adjacent to the motor) and compresses the air to thereby discharge the compressed air (compressed gas) to a discharge flow path 15 via a discharge port 14 (opening) on the other side in the axial direction (the side opposite to the motor).

The oil-injected (liquid-injected) compressor main unit 1 is configured to inject oil (liquid) into the compression chamber 9 on a suction stroke. The oil injected in the compression chamber 9 seals gaps in the compression chamber 9 (specifically, a gap between the male rotor 7 and the female rotor and a gap between the male rotor 7 or the female rotor and the casing 8) and cools the compressed air.

The male rotor 7 includes a tooth portion 16 having a plurality of spiral teeth, a suction-side shaft portion (motor-side shaft portion) 17 connected with one side in the axial direction of the tooth portion 16, and a discharge-side shaft portion (opposite-side shaft portion) 18 connected with the other side in the axial direction of the tooth portion 16. Similarly, the female rotor includes a tooth portion, a suction-side shaft portion, and a discharge-side shaft portion. The suction-side shaft portion 17 of the male rotor 7 is coaxially connected with the rotor shaft 3 of the motor 2 as described previously by being integrally molded with the rotor shaft 3 of the motor 2.

The tooth portion 16 of the male rotor 7 and the tooth portion of the female rotor are housed in a tooth portion housing chamber 19 of the main casing 10. The discharge-side shaft portion 18 of the male rotor 7 and the discharge-side shaft portion of the female rotor are housed in the main casing 10. The suction-side shaft portion 17 of the male rotor 7 and the suction-side shaft portion of the female rotor are housed in the suction-side casing 11.

The suction-side shaft portion 17 of the male rotor 7 is rotatably supported by a plurality of suction-side bearings 20. The discharge-side shaft portion 18 of the male rotor 7 is rotatably supported by a single discharge-side bearing 21. The suction-side bearings 20 are a plurality of angular ball bearings (specifically, combined angular contact ball bearings for face to face type or back to back type) and outer rings thereof are held at fixed positions in the suction-side casing 11 and inner rings thereof are fixed at fixed positions of the suction-side shaft portion 17 of the male rotor 7. The suction-side bearings 20 restrict axial movement of the suction-side shaft portion 17 of the male rotor 7 and bear a radial load and axial loads in both directions (specifically, a forward direction extending from the discharge side toward the suction side and a reverse direction extending from the suction side toward the discharge side).

The discharge-side bearing 21 is a cylindrical roller bearing (specifically, cylindrical roller bearing in which an outer ring or an inner ring has no flanges and the outer ring and the inner ring are axially movable relative to each other) and the outer ring thereof is held at a fixed position in the main casing 10 and the inner ring thereof is fixed at a fixed position of the discharge-side shaft portion 18 of the male rotor 7. The discharge-side bearing 21 bears a radial load, while permitting axial movement of the discharge-side shaft portion 18 as a result of thermal expansion of the male rotor 7.

Similarly, the suction-side shaft portion of the female rotor is rotatably supported by suction-side bearings 20. The discharge-side shaft portion of the female rotor is rotatably supported by discharge-side bearing 21.

Effects of the present embodiment will be described below.

In the present embodiment, the suction-side bearings 20 restrict axial movement of the suction-side shaft portion (motor-side shaft portion) of the male rotor 7 and the discharge-side bearing 21 permits axial movement of the discharge-side shaft portion 18 (opposite-side shaft portion) of the male rotor 7. Thus, a gap between a discharge-side end face of the tooth portion 16 of the male rotor 7 and a wall surface of the casing 8 is affected by the thermal expansion of the male rotor 7, but not by the thermal expansion of the rotor shaft 3 of the motor 2. Changes can thus be reduced in the gap between the discharge-side end face of the tooth portion 16 of the male rotor 7 and the wall surface of the casing 8. Similarly, changes can also be reduced in a gap between a discharge-side end face of the tooth portion of the female rotor and a wall surface of the casing 8. Thus, dimensions of the gaps described previously can be reduced to prevent leakage of compressed air and performance of the compressor main unit 1 can be enhanced.

A gap between the rotor 4A and the stator 5 and a gap between the rotor 4B and the stator 5 are affected by the thermal expansion of the rotor shaft 3 of the motor 2, but not the thermal expansion of the male rotor 7. Thus, changes can be reduced in the gap between the rotor 4A and the stator 5 and the gap between the rotor 4B and the stator 5. Thus, motor efficiency can be enhanced by setting dimensions of the foregoing gaps to optimum values and performance of the motor 2 can be improved.

Consider a case, as a comparative example, in which axial movement of the discharge-side shaft portion of the male rotor or the discharge-side shaft portion of the female rotor is restricted by a plurality of angular ball bearings and axial movement of the suction-side shaft portion of the male rotor or the suction-side shaft portion of the female rotor is restricted by a single cylindrical roller bearing. As compared with such a comparative example, the present embodiment can have the discharge-side shaft portion 18 of the male rotor 7 and the discharge-side shaft portion of the female rotor shorter in length. Thus, the compressor main unit 1 can be reduced in size. Or, because a degree of freedom in design of the discharge flow path 15 is increased, performance of the compressor main unit 1 can be enhanced.

Dimensions of the gaps in the present embodiment will be described below.

A dimension D of the gap between the discharge-side end face of the tooth portion 16 of the male rotor 7 and the wall surface of the casing 8 under a rated operation state (at high temperature) of the compressor is given by expression (1) given below, where Do denotes a dimension of the gap between the discharge-side end face of the tooth portion 16 of the male rotor 7 and the wall surface of the casing 8 under a stationary state (at room temperature) of the compressor (Do>D). Where, ΔLs denotes an amount of thermal expansion of the tooth portion 16 and ΔLb denotes an amount of thermal expansion of the tooth portion housing chamber 19 (ΔLs>ΔLb).

D=Do−(ΔLs−ΔLb)   (1)

Because D>0, the dimension Do of the gap between the discharge-side end face of the tooth portion 16 of the male rotor 7 and the wall surface of the casing 8 under the stationary state (at room temperature) of the compressor is given by expression (2) given below.

Do>ΔLs−ΔLb   (2)

A dimension Ma of the gap between the rotor 4A and the stator 5 under the rated operation state (at high temperature) of the compressor is given by expression (3) given below. Where, Mao denotes a dimension of the gap between the rotor 4A and the stator 5 under the stationary state (at room temperature) of the compressor and ΔMa denotes an amount of change in the dimension of the gap between the rotor 4A and the stator 5 (ΔMa>0).

Ma=Mao−ΔMa   (3)

A dimension Mb of the gap between the rotor 4B and the stator 5 under the rated operation state (at high temperature) of the compressor is given by expression (4) given below. Where, Mbo denotes a dimension of the gap between the rotor 4B and the stator 5 under the stationary state (at room temperature) of the compressor and ΔMb denotes an amount of change in the dimension of the gap between the rotor 4B and the stator 5 (ΔMb>0, ΔMb≈ΔMa).

Mb=Mbo+ΔMb   (4)

Because preferably Ma≈Mb holds, preferably the relation of expression (5) given below holds.

Mao>Mbo   (5)

The first embodiment has been described for an exemplary configuration in which the axial-gap motor 2 includes the two rotors 4A and 4B and the one stator 5 disposed between the rotors 4A and 4B. This configuration is, however, illustrative only and not limiting and various changes may be made therein without departing from the spirit and scope of the invention. Specifically, the axial-gap motor is only required to include at least one rotor and at least one stator disposed to be spaced apart from the rotor in the axial direction.

Specifically, as in a first modification depicted in FIG. 3, for example, an axial-gap motor 2A may include a rotor 4 mounted on a rotor shaft, a stator 5A disposed on an output side (side adjacent to a compressor main unit 1) with respect to the rotor 4, and a stator 5B disposed on a non-output side (side opposite to the compressor main unit 1) with respect to the rotor 4. Effects identical to the effects achieved by the first embodiment can be achieved even in the modification.

Dimensions of gaps in the present modification will be described. A dimension Mc of a gap between the rotor 4 and the stator 5A under the rated operation state (at high temperature) of the compressor is given by expression (6) given below. Where, Mco denotes a dimension of the gap between the rotor 4 and the stator 5A under the stationary state (at room temperature) of the compressor and ΔMc denotes an amount of change in the dimension of the gap between the rotor 4 and the stator 5A (ΔMc>0).

Mc=Mco+ΔMc   (6)

A dimension Md of a gap between the rotor 4 and the stator 5B under the rated operation state (at high temperature) of the compressor is given by expression (7) given below. Where, Mdo denotes a dimension of the gap between the rotor 4 and the stator 5B under the stationary state (at room temperature) of the compressor and ΔMd denotes an amount of change in the dimension of the gap between the rotor 4 and the stator 5B (ΔMd>0, ΔMc≈ΔMd).

Md=Mdo−ΔMd   (7)

Because preferably Mc≈Md holds, preferably the relation of expression (8) given below holds.

Mco<Mdo   (8)

The first embodiment has been described for an exemplary configuration in which the compressor main unit casing 8 includes the main casing 10 and the suction-side casing 11, which is coupled with the upper side (suction side) of the main casing 10. This configuration is, however, illustrative only and not limiting and various changes may be made therein without departing from the spirit and scope of the invention.

Specifically, as in a second modification depicted in FIG. 4, for example, a compressor main unit casing 8 may include a main casing 10A, a suction-side casing 11, which is coupled with an upper side (suction side) of the main casing 10A, and a discharge-side casing 22, which is coupled with a lower side (discharge side) of the main casing 10A. Then, the main casing 10A may house the tooth portions of the screw rotors and the discharge-side casing 22 may house the discharge-side shaft portions of the screw rotors and the discharge-side bearings. In such a modification, machining accuracy of the discharge flow path 15 can be enhanced compared with the first embodiment.

Additionally, in the first embodiment, the compressor main unit 1 has been described as an oil-injected type to compress air with injecting oil in the compression chamber 9. This configuration is, however, illustrative only and not limiting and various changes may be made therein without departing from the spirit and scope of the invention. Specifically, the compressor main unit may, for example, be a water-injected type (liquid-injected type) to compress air (gas) with injecting water (liquid) in the compression chamber 9. The same effects as those described above can be achieved in this case, too.

In the first embodiment, the screw compressor has been described for an exemplary configuration in which the screw rotors of the compressor main unit 1 and the rotor shaft 3 of the motor 2 extend in the vertical direction. This configuration is, however, illustrative only and not limiting and various changes may be made therein without departing from the spirit and scope of the invention. Specifically, the screw compressor may be configured such that the screw rotors of the compressor main unit and the rotor shaft of the motor extend in the horizontal direction. The same effects as those described above can be achieved in this case, too.

A second embodiment of the present invention will be described below with reference to FIG. 5. FIG. 5 is a vertical cross-sectional view of a configuration of a screw compressor according to the present embodiment of the present invention, depicting the rated operation state (high temperature state) of the compressor. In the present embodiment, like or corresponding parts are identified by the same reference numerals as those used in the first embodiment and descriptions for those parts will be omitted as appropriate.

The screw compressor in the present embodiment includes an oil-injected compressor main unit 1, an axial-gap motor 2 which drives the compressor main unit 1, and an oil separator 23 (gas-liquid separator) which separates oil (liquid) from compressed air (compressed gas) discharged from the compressor main unit 1. The compressor main unit 1, the motor 2, and the oil separator 23 are integrated with each other. Specifically, the compressor main unit 1 and the motor 2 are disposed vertically such that screw rotors of the compressor main unit 1 and a rotor shaft 3 of the motor 2 extend in the vertical direction. The motor 2 is disposed on an upper side (suction side) of the compressor main unit 1 and the oil separator 23 is disposed on a lower side (discharge side) of the compressor main unit 1.

The oil separator 23 includes an inner tube 24 and an outer tube casing 26. The inner tube 24 is disposed on a lower side of the compressor main unit 1. The outer tube casing 26 is integrally molded with a compressor main unit casing 8 and forms a swirl flow path 25 between a lower portion of the compressor main unit 1 and the inner tube 24. The swirl flow path 25 is connected with a discharge flow path 15 of the compressor main unit 1.

Compressed air discharged from the compressor main unit 1 is given a swirl in the swirl flow path 25 (see the arrow in FIG. 5), so that oil contained in the compressed air is centrifugally separated. The separated oil falls along the outer tube casing 26 and is collected in an oil storage portion 27 formed on a lower side of the outer tube casing 26. The oil collected in the oil storage portion 27 is supplied to a compression chamber 9 on a suction stroke by way of a flow path not depicted. Meanwhile, the compressed air from which the oil has been separated flows into an inside of the inner tube 24 and flows out through a flow path not depicted.

As in the first embodiment, in the present embodiment, too, suction-side bearings 20 restrict axial movement of the suction-side shaft portion (motor-side shaft portion) of the screw rotor and a discharge-side bearing 21 permits axial movement of the discharge-side shaft portion (opposite-side shaft portion) of the screw rotor. Thus, changes are reduced in the gap between the discharge-side end face of the tooth portion of the screw rotor and the wall surface of the casing and in the gap between the rotor and the stator of the motor, so that performances of the compressor main unit 1 and of the motor 2 can be improved.

Additionally, the discharge-side shaft portion of the screw rotor can be made shorter in length as in the first embodiment. This feature increases the degree of freedom in design of the discharge flow path 15 and the swirl flow path 25, so that performance of the compressor main unit 1 and performance of the oil separator 23 can be improved.

It is noted that, in the second embodiment, the screw compressor has been described as having a configuration including the oil-injected compressor main unit 1, which compresses air with injecting oil in the compression chamber 9, and the oil separator 23, which separates oil from the compressed air discharged from the compressor main unit 1. This configuration is, however, illustrative only and not limiting and various changes may be made therein without departing from the spirit and scope of the invention. Specifically, the screw compressor may include, for example, a compressor main unit that is a water-injected type (liquid-injected type) and a water separator (gas-liquid separator). The compressor main unit compresses air (gas) with injecting water (liquid) in the compression chamber 9. The water separator separates water from the compressed air (compressed gas) discharged from the compressor main unit. The same effects as those described above can be achieved in this case, too.

Additionally, the first and second embodiments have been described for a configuration in which a plurality of angular ball bearings (specifically, combined angular contact ball bearings for face to face type or back to back type) are employed as the suction-side bearings 20, which rotatably support the suction-side shaft portion of each screw rotor. This configuration is, however, illustrative only and not limiting and various changes may be made therein without departing from the spirit and scope of the invention. Specifically, any other type of rolling bearing may be employed when the suction-side bearings 20 restrict axial movement of the suction-side shaft portion of the screw rotor and support the radial load and the axial loads in both directions.

Specifically, as one suction-side bearing that rotatably supports the suction-side shaft portion of each screw rotor, a double-row angular ball bearing for face to face type or back to back type or a deep-groove ball bearing may be employed. Or, as a plurality of suction-side bearings that rotatably support the suction-side shaft portion of each screw rotor, a plurality of tapered roller bearings (specifically, combined tapered roller bearings for face to face type or back to back type) may be employed. Alternatively, as one suction-side bearing that rotatably supports the suction-side shaft portion of each screw rotor, a double-row tapered roller bearing for face to face type or back to back type may be employed.

Additionally, the first and second embodiments have been described for a configuration in which a cylindrical roller bearing is employed as a single discharge-side bearing that rotatably supports the discharge-side shaft portion of each screw rotor. This configuration is, however, illustrative only and not limiting and various changes may be made therein without departing from the spirit and scope of the invention. Specifically, any other type of rolling bearing may be employed when the discharge-side bearing permits axial movement of the discharge-side shaft portion of the screw rotor. Specifically, the rolling bearing may be held in the casing movably in the axial direction.

Additionally, the first and second embodiments have been described for an exemplary configuration in which the rotor shaft 3 of the motor 2 is integrally molded with the suction-side shaft portion 17 of the male rotor 7 to thereby be coaxially connected therewith. This configuration is, however, illustrative only and not limiting and various changes may be made therein without departing from the spirit and scope of the invention. Specifically, the rotor shaft 3 of the motor 2 may be coaxially connected with the suction-side shaft portion 17 of the male rotor 7 through a coupling. Alternatively, the rotor shaft 3 of the motor 2 may be coaxially connected with the suction-side shaft portion of the female rotor. In either case, the same effects as those described above can be achieved.

REFERENCE SIGNS LIST

1 Compressor main unit

2, 2A Motor

3 Rotor shaft

4, 4A, 4B Rotor

5, 5A, 5B Stator

7 Male rotor (Screw rotor)

8 Compressor main unit casing

9 Compression chamber

11 Suction-side casing

12 Suction port

14 Discharge port

17 Suction-side shaft portion (Motor-side shaft portion)

20 Suction-side bearing

23 Oil separator (Gas-liquid separator) 

1. A screw compressor including a liquid-injected compressor main unit that includes a screw rotor and compresses gas with injecting liquid in a compression chamber defined by a tooth groove of the screw rotor and an axial-gap motor that drives the compressor main unit, the screw rotor having a motor-side shaft portion connected coaxially with a rotor shaft of the motor, the screw compressor comprising: a bearing that rotatably supports the motor-side shaft portion of the screw rotor, wherein the bearing restricts axial movement of the motor-side shaft portion and bears a radial load and axial loads in both directions.
 2. The screw compressor according to claim 1, wherein the compression chamber of the compressor main unit draws in gas via a suction port on a side adjacent to the motor and discharges compressed gas via a discharge port on a side opposite to the motor, and the motor-side shaft portion is a suction-side shaft portion.
 3. The screw compressor according to claim 2, further comprising: a gas-liquid separator, disposed on a discharge side of the compressor main unit, for separating the liquid from the compressed gas discharged from the compressor main unit.
 4. The screw compressor according to claim 1, wherein the motor includes a first rotor disposed on an output side of the rotor shaft, a second rotor disposed on a non-output side of the rotor shaft, and a stator disposed between the first rotor and the second rotor, and a dimension of a gap between the first rotor and the stator is greater than a dimension of a gap between the second rotor and the stator at room temperature.
 5. The screw compressor according to claim 1, wherein the motor includes a rotor disposed on the rotor shaft, a first stator disposed on an output side with respect to the rotor, and a second stator disposed on a non-output side with respect to the rotor, and a dimension of a gap between the rotor and the first stator is smaller than a dimension of a gap between the rotor and the second stator at room temperature.
 6. The screw compressor according to claim 1, wherein the bearing includes combined angular contact ball bearings for face to face type or back to back type, and is held at a fixed position within a casing. 